Vortical gaseous-fluid type classifier for pulverized solid particles



W. A. THOMAS VORTICAL GASEOUS-FLUID TYPE CLASSIFIER @cfi. F11, 1949.

FOR PULVERIZED SOLID PARTICLES 3 Sheets-Sheet 1 Filed Feb. 15, 1946 V wwGet. 11, 1949. w. A. THOMAS VORTICAL GASEOUS-FLUID TYPE CLASSIFIER FORPULVERIZED SOLID PARTICLES 3 Sheets-Sheet 3 Filed Feb. 15, 1946 BY m, MK

Patented Oct. 11, 1949 UNITED STATES FATE.

VORTICAL GASEOUS-FLUHD TYIE CLASSI- FIER FOR PULVERIZED SOLID PAR'EKCLESWilliam A. Thomas, Pittsburgh, Pa, assigno r to Blew-Knox Company,Pittsburgh, Pa, a cor poration of New Jersey Application February 15,1946, Serial No. 647,670

6 @laims. i This invention relates to the grinding or pulverizing ofsolids in an intermediate state of subdivision by impact of theparticles with each other and the walls of an endless passage throughwhich they are driven by a suitable motive fluid. In particular, theinvention relates to means for separating the particles which have beenreduced to sufficiently small size from the remainder of the circulatingparticles and delivering them to a point of use while returning theoversize particles for further grinding.

Impact grinders or pulverizers of the endlesspassage type have beenknown for some time but have been found to be subject to seriouslimitations in respect to capacity, the amount of steam required and thecontrol of the size of the prodnot. In addition, the delivery of theproduct is pulsating and not continuous. It is impossible to pulverizematerial having a substantial moisture content in the known apparatusand the latter requires considerable time for gradual shutdown.

I have invented a novel pulverizing apparatus which avoids theaforementioned objections to apparatus of the same general type knownheretofore. In a preferred embodiment, I provide a pulverizer of thecontinuous-passage type with a classifier adapted to be connected incircuit therewith, capable of separating the particles which. have beenreduced sufilciently in size from those which require further grinding.The classifier preferably comprises a housing adapted to be connected tothe members forming the continuous passage of the grinder or pulverizerso that a descending stream of gas with particles entrained therein isdelivered to the top of the classifier. A spreader cone is located inthe upper portion of the housing and has a cylindrical baffle or skirtdepending therefrom. An outlet duct leads from the cone to the exteriorof the housing. A hopper located below the cone and within the bafflecollects oversize particles and returns them to the pulverizer. A seriesof vertical guide vanes spaced around the interior of the baffle imparta circumferential velocity component to the inwardly flowing gas,thereby fa- ,cilitating separation of the oversize particles from thosewhich have been sufiiciently reduced in size. The latter float in thegas and are conveyed by the outflowing stream thereof through the outletduct.

A complete understanding of the invention may be obtained from thefollowing detailed description when read in connection with theaccompanying drawings illustrating the preferred embodiment. In thedrawings,

Figure 1 is a side elevation showing the invention in operative relationto means for supplying solid fuel to be ground and means for delivtringthe ground fuel to a combustion space;

'larged scale, partly broken away and partly in- Cal . portion of thegrinder.

Figure 2 is an elevation of the grinder to ensection along a centralvertical plane;

Figure 2a is a vertical section through an injector for delivering tothe grinder the material to be ground;

Figures 3 and 4 are transverse sectional views taken along the plane oflines III-J11 and IV--IV, respectively, of Figure 2; and

Figure 5 is a partial vertical section taken through the outlet duct.

Referring now in detail to the drawings and, for the present, to Figure1, solid material to be ground, in the particular applicationillustrated, coal or a suitable grade, is stored in a bin ill from whichit is delivered by a screw conveyor ll to the inlet I 2 of an injectorit. A motor-reducer llla drives the conveyor and an agitator Na in thebin iii.

The injector it delivers the coal into the upperportion of an impactgrinder it of the endlesspassage type shown in Figures 6 and 7 ofKidwell Patent 2,219,011. The grinder includes a classifier it fromwhich coal of the desired degree of fineness flows through pipe it to aseparator l'l, being entrained ina stream of motive fluid such a steam.The separator delivers the coal downwardly to a burner it from which itis discharged into a combustion space it) by a stream of air deliveredto the burner from a blower 20 through suitable piping 2i. The steamfrom which the coal has been largely separated is discharged from theseparator through a pipe 22 to the combustion space.

The classifier i5 is illustrated in detail in Fig ures 2 through 4 alongwith the injector l3 and the pulverizer it. The injector includes aVenturi throat 23 between the inlet l2 and the upper A scraper 25 ismounted for rotation in the inlet it about the axis of the steam nozzle25 of the injector to prevent accumulation of material at the entranceend of the Vc-nturi throat. The shaft of the agitator Ha is prolongedand drives the scraper 25 in the inlet l2 through bevel gears 122). Thisportion of the apparatus is disclosed in greater detail and claimed inmy copending application Serial No, 637,819 filed December 29, 1945,Patent No. 2,420,- 388, for Apparatus for feeding granular material intoa fluid stream.

The injector discharges coal into the upper portion of the grinder M.The lower portion of the grinder is formed by a jet tube 24 which is anelbow having steam nozzles 28 spaced therealong adapted to deliver jetsfor driving the coal particles repeatedly around the grinder I l. Thelatter also includes an arcuate tube 29 with a connection for theinjector, and connecting members 30 and 3!,

These several members form a continuous passage the sectional area ofwhich increases gradually in the direction of the flow.

The classifier l5 comprises a housing 32 having its upper end connectedto the outlet end of the tube 29 and its lower end to the entrance endof apart and a cylindrical wall therebetween. A

spreader 33 in the form of a conical frustum is disposed in the upperportion of the housing and has a cylindrical baille or skirt 34depending from the lower edge thereof. A renewable wear plate 33a isplaced on the frustum to withstand the impact of particles emerging fromtube 23. A hopper 35 is supported in the lower portion of the housing onradial brackets 36. A series of vertical guide vanes 31 is disposedbetween the hopper and the spreader cone. The vanes have vertical hingepins, the lower ends of which are journaled in a ring 38 carried by thehopper. The upper ends of the hinge pins are journaled in a base plate39 secured to the cone 33. The cone 33 and baille 34 are thus supportedon hopper 35. A ring 40 rests on the upper ends of the vanes 31.Projections 4| at the inner edges of the vanes extend into radial slots42 spaced circumferentially of the ring 40. It is thus possible toadjust all the vanes 3! simultaneously by rotating the ring 40. For thispurpose, the hinge pin of one of the vanes has an extension 43projecting downwardly therefrom and through the lower portion of thehousing. A lever 44 permits the extension 43 to be turned by hand foreffecting the desired adjustment of the vanes 31.

The base plate 39 has a central opening therethrough from which atubular neck 45 depends. An outlet passage 46 extends from the cone 33to the adjacent wall of the housing and connects with an elbow 41. Asshown vin Figure 1, the delivery pipe l6 communicates with this elbow. Ahelical flight or vane 48 extends around inside the hopper 35 to causethe particles and steam moving circumferentially of the hopper todescend through the open'lower end thereof and re-enter the tube 24 ofthe pulverizer.

The operation of the apparatus is as follows. Coal introduced into thetube 29 by the injector I3 is subjected to impact the plate 33a and,after passing the classifier l5 with the result to be explained, againstthe walls of the endless passage formed by. the members 24, 29, 30 and3| of the grinder H. The particles are driven along a continuous courseby the jets from the nozzles 28 and are delivered by entrainment in theresulting stream to the upper end of the housing 32. The stream of steamand coal particles striking the plate 33a and cone 33 are spreadlaterally in all directions. Some of the steam and the finer particlesentrained thereby flow around the lower edge of the baflie 34 andinwardly between the vanes 31 toward the central outlet through neck 45.As the steam passes around the lower edge of the baflie 34, the largerand heavier particles continue on a downward course falling into thelower portion of the housing and returning to the entrance of the tube24. The steam and particles which pass between the vanes 31 have acircumferential motion imparted thereto by the angular adjustment of thevanes whereby a vortex is created in the upper portion of the hopper 35.From the center of the vortex a column of steam ascends through the neck45 carrying with it the particles of coal which have been reduced tosuch a size as to float in the outflowing stream. The

4 stream flows from the cone 33 through the outlet 46, through elbow 41and thence by pipe is to the separator l I. The larger, heavierparticles which pass between the vanes 31 fall downwardly as they travelabout the hopper. 0n striking the helical vane 48, these particles aregiven a positive downward velocity component and are thereby dischargedinto the entrance end of the tube 24.

It will thus be apparent that the device effects a two-stage separationof the coal which has been sufllciently reduced in size for combustion.The first separation occurs when a portion of the steam entering theclassifier sweeps around the lower edge of the baiile 34. The secondstage occurs within the hopper 35, as a result of the circumferentialvelocity component imparted to the steam and entrained coal particles bythe angular adjustment of the vanes 31.

The mixture of steam and coal particles delivered to the separator IIfrom the classifier i5 is divided thereby into a stream of finelydivided coal falling into the burner is and a stream of steam with asmall percentage of coal delivered through pipe 22 into the combustionspace IQ.

The helical vane 48 is an important feature of the classifier because itproduces a down draft of steam and oversize particles through the hopper35, thus preventing an up draft through the hopper which might tend tobe produced by direct flow of steam around the cone 33, the baille 34and the hopperand into the bottom of the latter.

The operation of the classifier may be summarized thus. In the spacebetween the housing and the bailie 34, the coarser particles areseparated by the differential in their mass weight as a result of theirinertia. This separation is possible because of the reduced velocity ofthe steam resulting from the large sectional area of the annular passagethrough the classifier as compared to that of the passage through thegrinder. The coarse particles continue undeflected and reenter thegrinder for further reduction in size. The steam carrying the smallerparticles rises inside the baflle 34 and is subjected to a secondseparation resulting from the tangential motion imparted by the vanes31. In this centrifugal separation, the finest particles float on theascending stream through the outlet while the coarser particles circlearound in the hopper and are positively directed downwardly by the vane48.

The apparatus of my invention has several important advantages overimpact pulverizers as known heretofore. In the first place, I amenabled, by my invention, to deliver a greater quantity of finely groundmaterial than has been obtainable heretofore from continuous-passageimpact grinders. This seems to result from the fact that the velocity ofthe circulating steam is reduced in the region where the separationoccurs as a result of the enlargement of the sectional area of thepassage. My invention also makes it possible to grind a given amount ofmaterial with a smaller amount of steam. The delivery of the finelyground material, funthermore, is steady and continuous, and free fromthe pulsations characterizing the operation of apparatus known before.The apparatus of my invention is also capable of pulverizing materialshaving a substantial moisture content. This was impossible with theprior apparatus. It is also possible to shut down the pulverizeraccording to my invention much more quickly than those known previously.

My invention also has the characteristic of delivering material ofsubstantially the same degree of fineness regardless of the rate offeed. This is not true of previous grinders which exhibited a markedchange in the fineness of the product if the feed rate is changedmaterially, the particle size becoming larger as the feed rate isincreased. On the contrary, the apparatus of my invention exhibited butvery small changes in the percentages of various sizes of particles whenthe feed rate was varied over a substantial range. This is particularlyimportant in combustion applications since it is frequently desirable tooperate at reduced rates without affecting combustion conditionsseriously. Considering the entire system as applied to the production ofpulverized coal for combustion, the removal of steam in the separatorpermits cold air to be supplied to the burner without objectionablecondensation.

The location of the feed-in connection above the classifier increasesthe rate of grinding which is particularly important in the case of theharder coals. It also gives better drying of the coal and pulverizer ofthe endless-passage type delivering downwardly therefrom a stream of gasentraining particles of various sizes, said classifier comprising ahousing converging toward its upper and lower ends, said ends beingconnected to points spaced apart along the pulverizer and iorming aportion of said endless passage, a fixed some initial separation offines because the entering coal makes one pass through the classifierbefore grinding begins (except that due to striking the plate 33a).

Fundamentally, my invention makes it possible to withdraw from thegrinder substantially all the material which has been ground to thedesired fineness. It difiers in this respect from grinders previouslyknown in which it was impossible to withdraw a substantial portion ofthe material which had been sufiiciently reduced in size. In theembodiment illustrated, my invention removes from the grinder all coalwhich is in a state of subdivision suificiently small for use .aspulverized fuel. M invention is not only capable of being shut down morequickly than previous grinders but also makes it possible to start upcombustion in a much shorter time.

While the invention has been described by reference to a system for theproduction of pulverized coal for combustion, it will be understood thatthis is merely by way of example since the apparatus may be used forgrinding material other than coal.

Although I have illustrated and described but a preferred embodiment ofmy invention, changes in the details of construction disclosed may bemade without departing from the spirit of the invention or the scope ofthe appended claims.

I claim:

1. In combination, a classifier for separating particles of granularmaterial adapted to be connected in c.osedcircuit relation with animpact pulverizer of the'endless-passage type delivering downwardlytherefrom a stream of gas entraining particles of various sizes, saidclassifier comprising a housing converging toward its upper and lowerends, said ends being connected to points spaced apart along thepulverizer and forming a portion of said endless passage, a downwardlyflaring spreader cone in the upper portion of the housing adjacent thegaseous fluid inlet thereto, a skirt depending from the cone,

2. series of vertical guide vanes spaced around the skirt and spacedinwardly thereof, a passage between said vanes and the interior of saidcone, an outlet leading from said interior of said cone to the exteriorof said housing, and a hopper in the lower portion of said housing andbelow said guide vanes for returning oversize particles to thepulverizer.

2. In combination, a classifier for separating particles of granularmaterial adapted to be connected in close-circuit relation with animpact downwardly flaring spreader cone in the upper portion of thehousing adjacent the gaseous fluid inlet thereto, a series of verticalguide vanes for said gas-entrained particles spaced around the axis ofthe cone and lying below the cone and within the projection of the basethereof on a horizontal plane, said guide vanes being angularly disposedwith respect to the respectively adjacent radii of said cone, a passagebetween said vanes and the interior of said cone, an outlet leading fromsaid interior of said cone to the exterior of said housing and a hopperin the lower portion of said housing and below said guide vanes forreturning oversize particles to the pulverizer.

3. In combination, a classifier for separating particles of granularmaterial adapted to be installed in a descending stream of gasentraining particles of various sizes in an impact pulverizer of theendless-passage type, comprising, a housing for said classifier forminga portion of said endless passage, a fixed downwardly flaring spreadercone in said housing adjacent the gaseous fiuid inlet thereto, acylindrical baflle coaxial with said cone and extending downwardlytherefrom, a passage extending between the interior of said baffle andsaid cone, an outlet duct communicating with said cone for conductingoutflowing gas and particles floating therein, a hopper within saidbafiie coaxial therewith and smaller in diameter than the bafile forcollecting oversize particles falling through the gas, guide vanes forsaid gas entrained particles above the hopper for directing the gasentering the space between it and the baifie in a directioncircumferentially of the hopper, and an opening in the bottom of saidhopper through which said oversize particles are returned to thematerial passing through said endless passage beyond said classifier.

4. In combination, a classifier for separating particles of granularmaterial adapted to be connected in closed circuit relation with animpact pulverizer of the endless-passage type delivering downwardlytherefrom a stream of gas-entrained particles of various sizes,comprising, a housing forming an enlarged portion along the length ofsaid axial passage, 9. fixed frusto-conical spreader concentricallypositioned within said housing adjacent the gaseous fiuid inlet thereto,a cylindrical skirt substantially depending from the lower edge of saidspreader, a hopper concentrically positioned within said cylindricalskirt and spaced therefrom, a depending tubular neck positioned withinsaid spreader in concentric relation thereto and above said hopper,means defining a plurality of generally radial passages extendingbetween the interior surface of said skirt and the interior of saidhopper adjacent the upper portion thereof an outlet in communicationwith said tubular neck and extending through said housing, a downwardlydirecting helical vane in the lowermost portion of said hopper, saidhopper having an axial opening below said vane, whereby gas-entrainedfineparticles make a reentrant turn beneath said skirt and enters saidhopper wherein the predetermined finer portion thereof passes outthrough said neck and said outlet and the coarser portion thereof passesout through said opening at the bottom of said hopper to rejoin materialmoving through said endless passage.

'5. In combination, a classifier for separating particles of granularmaterial adapted to be con- 1 nected in closed circuit relation with animpact pulverizer of the endless-passage type delivering downwardlytherefrom a stream of gas-entrained particles of various sizes,comprising, a housing extending between the base of said spreader andthe interior of said hopper adjacent the upper portion thereof, saidannular passage being above the bottom of said tubular neck, centrifugalguiding means in said annular passage, and an outj let in communicationwith said tubular neck'and extending through said housing, said hopperhaving an axial opening in the bottom thereof, whereby gas-entrainedfine particles enter said hopper beneath said spreader with a whirlingmotion and make a reentrant turn around the bottom of said neck whereinthe predetermined finer portion thereof passes out through said neck andsaid outlet and the coarser portion thereof passes out through saidopening at the bottom 1 of said hopper to rejoin material moving throughsaid endless passage.

6. In combination, a classifier for separating particles of granularmaterial adapted to be connected in closed circuit relation with animpact pulverizer of the endless-passage type delivering downwardlytherefrom a stream of gas-entrained particles of various sizes,comprising, a housing forming an enlarged substantially vertical portionalong the length of said axial passage, a fixed frusto-conical spreaderconcentrically positioned within said housing adjacent the gaseous fluidinletthereto, a hopper ooaxially positioned beneath said spreader andspaced therefrom, a depending tubular neck positioned beneath saidspreader in concentric relation thereto and above said hopper, meansdefining an annular passage extending between the base of said spreaderand the interior of said hopper adjacent the upper portion thereof, saidannular passage being above the bottom of said tubular neck, centrifugalguiding means in said annular passage, an outlet in communication withsaid tubular neck and extending through said housing, said hopper havingan axial opening in the bottom thereof, and a downwardly directinghelical vane around the inside of said hopper adjacent said axialopening, whereby gas-entrained fine particles enter said hopper beneathsaid spreader with a whirling motion and make a reentr ant turn aroundthe bottom of said neck wherein the predetermined finer portion thereofpasses out through said neck and said outlet and the coarser portionthereof passes out through said opening at the bottom of said hopper torejoin material moving through said endless passage.

WILLIAM A. THOMAS.

REFERENCES CITED I The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,058,313 Luckenbach Apr. 8,19131,367,635 Sturtevant Feb. 8, 1921 1,569,468 Ely Jan. 12, 1926 1,635,527Barthelmess July 12, 1927 1,698,361 Dreisback Jan. 8, 1929 1,770,850Hartman July 15, 1930 2,010,128 Arnold Aug. 6, 1935 2,055,385 NoackSept. 22, 1936 2,219,011 Kidwell et a1 Oct. 22, 1940 2,224,169 TurnbullDec. 10, 1940 FOREIGN PATENTS Number Country Date 806,771 France Oct. 5,1936 590,866 Germany Oct. 13, 1930 Certificate of Correction Patent No.2,484,255 October 11, 1949 WILLIAM A. THOMAS It is hereby certified thaterrors appear in the printed specification of the above numbered patentrequiring correction as follows:

Column 2, line 27, for the words a steam read as steam; column 8, line46, list of references cited, for the foreign patent number 590,866 read509,866;

and that the said Letters Patent should be read with these correctionstherein that the same'may conform to the record of the case in thePatent Ofiice.

Signed and sealed this 7th day of February, A. D. 1950.

THOMAS F. MURPHY,

Assistant Oommz'ssz'omr of Patents.

